1. Field of the Invention
The present invention relates to a novel process for producing a high-content product of 2-O-xcex1-D-glucopyranosyl-L-ascorbic acid (hereinafter abbreviated as xe2x80x9cxcex1G-AAxe2x80x9d, unless specified otherwise), a stabilized L-ascorbic acid.
2. Description of the Prior Art
As disclosed in Japanese Patent Kokai No. 183,492/91, xcex1G-AA is known to have the following satisfactory physicochemical properties:
(1) It is not directly reducible, but has outstandingly high stability, and, unlike L-ascorbic acid, it does not cause a Maillard reaction and unnecessary reaction even when in the presence of amino acids, peptides, proteins, lipids, saccharides, or physiologically active substances, but it stabilizes them;
(2) Upon hydrolysis, it forms L-ascorbic acid, then exhibits substantially the same reducing and anti-oxidation actions as L-ascorbic acid;
(3) It is easily hydrolyzed by in vivo enzymes into L-ascorbic acid and D-glucose to exhibit the physiological activities inherent to L-ascorbic acid, and is capable of enhancing the physiological properties of vitamins E and P when used in combination;
(4) It is highly safe because it is naturally formed in a slight amount though and, when orally taken, it is metabolized in vivo into L-ascorbic acid and a substance such as an xcex1-glucosyl saccharide compound;
(5) Although xcex1G-AA in a crystalline form is non- or substantially non-hygroscopic, it has a relatively-high solubility rate and solubility in water, and thus it can be advantageously used as a vitamin C-enriching agent, taste improver, acid-imparting agent, or stabilizer for vitamin preparations in the form of a powder, granule or tablet; and used in foods and beverages such as sand creams, chocolates, chewing gums, instant juices, and instant seasonings; and
(6) It has satisfactory handleability because xcex1G-AA in a crystalline form is non- or substantially non-hygroscopic and keeps its free-flowing ability without solidification during storage. As compared with xcex1G-AA in a non-crystalline form, xcex1G-AA in a crystal form can highly cut physical and labor costs required in its package, transportation, and storage.
xcex1G-AA is now widely used in a cosmetic field mainly and is expected for its explorative use in other various fields such as food products, pharmaceuticals, feeds, pet foods, and industrial materials.
As a representative example of industrial process for producing xcex1G-AA is, for example, a process as disclosed in Japanese Patent Kokai No. 183,492/91. The process, as shown in FIG. 1, comprises the steps of contacting a solution containing L-ascorbic acid and an a-glucosyl saccharide compound(s) with a saccharide-transferring enzyme or glucoamylase (EC 3.2.1.3) to form xcex1G-AA to obtain a solution comprising xcex1G-AA, intact L-ascorbic acid, xcex1-glucosyl saccharide compound(s) and other saccharides produced from the xcex1-glucosyl saccharide compound(s) filtering the resulting solution; removing minerals from the filtrate by subjecting the filtrate to column chromatography using a cation-exchange resin (H-form); subjecting the demineralized solution to column chromatography using an anion-exchange resin to adsorb xcex1G-AA and L-ascorbic acid on the anion-exchange resin; washing the anion-exchange resin with water to remove saccharides from the column; eluting the xcex1G-AA and the L-ascorbic acid from the anion-exchange resin; concentrating the eluate; subjecting the concentrate to column chromatography using a strong-acid cation exchange resin to fractionate into a fraction rich in xcex1G-AA and a fraction rich in L-ascorbic acid; and concentrating the former fraction into a high xcex1G-AA content product.
In the above column chromatography using an anion-exchange resin, xcex1G-AA and L-ascorbic acid are simultaneously desorbed from the resin, and this yields xcex1G-AA in a mixture form with L-ascorbic acid. To obtain a high xcex1G-AA content product, solutions containing xcex1G-AA and L-ascorbic acid should inevitably be first concentrated, then fractionated into a fraction rich in xcex1G-AA and a fraction rich in L-ascorbic acid
As described above, in conventional process for producing high xcex1G-AA content product, two steps of column chromatography using an anion-exchange resin and a cation-exchange resin are inevitably required, and the eluate from the column chromatography using the anion-exchange resin should be first concentrated before fed to column chromatography using the cation-exchange resin, and, as the demerits, these complicate the preparation of xcex1G-AA, lower the yield of high xcex1G-AA content products, and increase the production cost.
Under these circumstances, there has been in a great demand an industrial-scale production of high xcex1G-AA content products with relatively-high quality and satisfactory processibility, production cost, and yield.
The object of the present invention is to provide an industrial-scale production of high xcex1G-AA content products with relatively-high quality and satisfactory processibility, production cost, and yield. The term xe2x80x9chigh xcex1G-AA content product(s)xe2x80x9d as referred to in the present invention means high xcex1G-AA content product(s) which contain(s) at least 80% (w/w) of xcex1G-AA (xe2x80x9c% (w/w)xe2x80x9d may be abbreviated as xe2x80x9c%xe2x80x9d, hereinafter) on a dry solid basis (d.s.b.), preferably, at least 90%, and which may have any form of a liquid, paste, solid or powder.
In view of the foregoing, the present inventors continued studies on a simpler process for producing high xcex1G-AA content products by contacting a solution containing xcex1G-AA and L-ascorbic acid with an ion-exchange resin packed in a column. As a result, they found that the object can be attained by using an anion-exchange resin as an ion-exchange resin to be packed in a column; allowing xcex1G-AA and L-ascorbic acid to adsorb on the anion resin; feeding to the column an aqueous solution, as an eluent, of an acid and/or a salt with a concentration of less than 0.5 N to fractionate into a fraction rich in xcex1G-AA and a fraction rich in L-ascorbic acid; and collecting the former fraction.
As shown in FIG. 2, the process for producing high xcex1G-AA content product according to the present invention is characterized in that it comprises the steps of allowing a saccharide-transferring enzyme with or without glucoamylase to act on a solution containing L-ascorbic acid and an xcex1-glucosyl saccharide compound(s) to obtain a solution containing xcex1G-AA, L-ascorbic acid, and saccharides; filtering the solution; demineralizing the filtrate; contacting the demineralized solution, as a material solution, with an anion-exchange resin packed in a column to adsorb on the resin xcex1G-AA and L-ascorbic acid; washing the resin with water to remove saccharides from the column; feeding an aqueous solution of an acid and/or a salt with a concentration of less than 0.5 N to fractionate a fraction rich in xcex1G-AA and a fraction rich in L-ascorbic acid; and concentrating the former fraction to obtain a high xcex1G-AA content product. According to the present invention, xcex1G-AA, and L-ascorbic acid can be separated by column chromatography using an anion-exchange resin, resulting in a cancellation of the column chromatography using a strong-acid cation exchange resin which is inevitably used in a conventional preparation as shown in FIG. 1. As a result, relatively-high quality products rich in xcex1G-AA with advantageous processibility, economical viewpoint, and yield can be produced in an industrial scale.